The development of optical telecommunications has demonstrated the advantage of implementing wavelength-multiplexed transmissions. Thus, different luminous fluxes, each able to carry a different content of information, must transit over the same wave-guide, for example over the same optical fiber. The transmission capacities of the same hardware means, composed essentially of the optic fiber are thus enhanced considerably.
Until now, to provide this multiplexing, several sources have been used generally, each transmitting at a certain wavelength that is unique. Their coupling is ensured in a unique fiber via a multiplexer. This arrangement is often satisfactory. However, this arrangement involves multiplying the number of sources and hence of each of their components and resorting to a multiplexer that collects the luminous fluxes transmitted by the different sources and coupling them to a given fiber.
A system of optical communications has been suggested (Patent Abstract of Japanxe2x80x94JP-A-56.090,642) comprising several solid-state lasers associated with a unique retroreflecting device. This retroreflecting device xe2x80x9cseesxe2x80x9d each of these lasers from a different angle and forms with the same angle a different cavity. Each source thus formed transmits at a unique wavelength. This arrangement enables, with respect to completely disconnected systems, limiting the number of necessary components, but calls for the use of a multiplexer in order to couple the fluxes transmitted by these sources in a fiber.
From GB-A-2.202.404 patent application, a device supplying a multiwavelength laser source is known, ensuring coupling the various transmission wavelengths in a unique output fiber. This device comprises lasers associated with an external cavity enabling each of them to resonate at a different wavelength and coupling the fluxes generated in an optic fiber.
This document GB-2.202.404 indicates that the laser, as any external cavity laser, even single wave-guide external cavity laser, may resonate over several longitudinal modes. Conventionally, it is suggested to obviate this drawback by using a reference structure. This structure is formed in the output fiber, i.e. in a zone where the beams are superimposed spatially.
However, in a multiwave-guide external cavity source, in addition of, or instead of the wavelengths desired, interference wavelengths may be generated. This may result that, in addition to the selection provided by the cavities that correspond to a determined wave guide to a single two-way travel of the beam between this wave-guide and the external reflector, such a device also forms cavities corresponding to several two-way travels of the beam between several amplifier guides and the external reflector. In a particular laser, the amplifier medium is thus capable of resonating at several wavelengths accepted by the external cavity. Such a conflict between modes is obviously detrimental and prevents the source from operating correctly.
One aim of the invention is to provide a multiwavelength source that does not exhibit these defects and whose operation is, generally, optimized.
To this end, the inventive relates to a multiwavelength laser source transmitting a luminous flux comprising as many amplifier wave-guides as potential transmission wavelengths, a collimation optic system for collimating the beams transmitted by the wave-guides, a network and a retroreflective making up with the network, a dispersive retroreflecting device that defines with each wave-guide an external resonating cavity, whereby each wave-guide has an inner face and an outer face with respect to its associated cavity.
According to the invention, a Fabry-Perot interferometer where reduced fine adjustment is placed in the cavity between the collimation optic system and the grating, whereby the said interferometer is tilted with respect to the axis of the cavity and forms a little selective filter, whose variation law of the wavelength transmitted in relation to the angle of incidence is identical with that of the dispersive retroreflecting device.
According to various embodiments, each exhibit particular and unable advantages in all technically possible combinations:
the resonating external cavity is in the Littman-Metcalf configuration;
the luminous flux transmitted is collected via the retroreflector and coupled in a single output monomode fibre;
the retroreflector is a mirror;
the retroreflector is a self-aligned system;
the retroreflector is a dihedron;
the retroreflector comprises a cylindrical lens and a partially retroreflecting mirror;
a prism arranged between the grating and the collimation optic system provides linear distribution of the frequencies of the luminous fluxes generated by the source;
the amplifier wave-guides are identical with one another;
the wave-guides are made over the same solid state substrate;
the inner face of each wave-guide has an anti-reflecting coating;
the outer face of the wave-guides is 100% reflecting.